1. Technical Field of the Invention
The present invention relates to mobile terminal devices such as mobile telephones, PDAs (personal digital assistants), tablet PCs, electronic book readers, more specifically to mobile terminal devices including telephone communication functions. In addition, the present invention relates to storage media used in such mobile terminal devices to hold preferred computer programs, and sound output control methods preferably used in the mobile terminal devices.
2. Disclosure of the Related Art
Conventionally, each mobile telephone has a speaker and a microphone for telephone communications on one surface of the device main body. During telephone communications, a user holds the telephone communication speaker close to his/her ear to hear voices from a communication partner.
To provide users with clear sounds, it is conceivable to employ a so-called cartilage-conduction speaker as a speaker for telephone communications on such a mobile telephone.
The cartilage-conduction speaker includes a vibration plate such as a piezoelectric vibration element, and uses the vibration plate to vibrate one surface of the device main body. When a user brings one surface of the device main body into contact with his/her ear, the user's auricular cartilage is vibrated by the vibrations of the one surface, and the vibrations of the auricular cartilage are transferred to his/her eardrum to vibrate the eardrum. Accordingly, the user's brain recognizes sounds.
A mobile telephone with such a cartilage-conduction speaker generates sound waves by vibrations of one surface of the device main body. The user can also recognize sounds by transfer of the sound waves to his/her eardrum. However, the sound pressure of generated sound waves is low at the cartilage-conduction speaker.
When a mobile telephone includes a cartilage-conduction speaker, the user can hear clear sounds by holding the device main body in contact with his/her ear. However, it is not easy for the user to hold the device naturally in constant contact with his/her ear during telephone communications. When the device main body is separated from his/her ear, transfer of sounds via the auricular cartilage is interrupted. Although sounds are transferred by sound waves, the user cannot easily hear the sounds due to a low sound pressure.
Depending on sound information obtained during telephone communications, in some cases, it is more undesired that transfer of sounds is interrupted due to separation of the device main body from a user's ear.